TWI892339B - Mirror arrangement for absorbing radiation, and lithography system - Google Patents

Abstract

The invention relates to a mirror arrangement, in particular for a lithography system (1), comprising: a plurality of mirror elements (23) for reflecting radiation (16), a plurality of carrier elements (24), which each carry one of the mirror elements (23), and a mount arrangement (25) having insert openings (26) formed in each case to accommodate a respective one of the carrier elements (24), with the plurality of carrier elements (24), which each carry one of the mirror elements (23), being accommodated in the insert openings (26) of the mount arrangement (25). For absorbing radiation (16), at least one of the insert openings (26) does not accommodate a carrier element (24) and/or, for absorbing radiation (16), at least one of the insert openings (26) accommodates a dummy carrier element (24’) which does not carry a mirror element (23).

Description

Radiation absorbing mirror device and lithography system

The present invention relates to a mirror arrangement, in particular a mirror arrangement for a lithography system, comprising: a plurality of mirror elements for reflecting radiation; a plurality of carrier elements, each of which carries one of the mirror elements; and a mounting device having insertion openings formed in each case to accommodate opposite ones of the carrier elements, wherein the plurality of carrier elements, each of which carries one of the carrier elements, are accommodated in the insertion openings of the mounting device. The invention also relates to a lithography system having at least one such mirror arrangement.

A lithography system may be a lithography apparatus for exposing wafers or some other optical device used in lithography, such as an inspection system, for example, for inspecting masks, wafers, (mirror) components, etc. used in lithography. A lithography system may be embodied for EUV lithography, for example in the form of an EUV lithography apparatus used in the production of semiconductor devices and operating with short-wavelength radiation (so-called EUV radiation), operating at a wavelength between approximately 5 nm and 30 nm.

Heat is generated in lithography systems, especially EUV lithography equipment, due, among other things, to absorption of EUV radiation, heating of optical elements in the form of mirrors, and friction losses during actuator movement. The heat generated during operation of the lithography system can be dissipated by cooling the components of the lithography system.

For example, the component to be cooled can be a mirror element in the form of a micromirror array, particularly a microelectromechanical mirror module ("MEMS mirror module"). A MEMS mirror module comprises a plurality of micromirrors arranged in a grid, which can typically be actuated or tilted about at least one axis, and preferably about two axes. In each case, the micromirrors are very small components (e.g., approximately 1 ^mm² per mirror surface) and are controlled or actuated using chip-based logic and micromechanical structures. Actuation of the micromirrors of the corresponding mirror module is accompanied by the release of heat, which is difficult to dissipate due to the small size of the micromirrors or their mounting method.

Patent document DE 10 2013 205 214 B4 describes a micromechanical or microelectromechanical tool for projection exposure equipment, comprising at least one micromechanical or microelectromechanical component and a temperature control device including a gas supply and a gas extraction member. The at least one micromechanical or microelectromechanical component is enclosed in a housing having a gas supply line, a gas exhaust line, and at least one window for the working light of the projection exposure equipment. Specifically, the tool can be a multi-mirror device having a plurality of electromechanical micromirrors.

Patent document DE 10 2014 219 770 A1 describes a mirror device comprising: at least one mirror element, which carries a mirror surface configured to reflect electromagnetic radiation; at least one carrier element, which comprises a head portion and a seat portion configured to accommodate the at least one mirror element; and a mounting device for accommodating the at least one carrier element. At least one insertion opening is formed in the mounting device, and the seat portion of the carrier element is immersed in the insertion opening. A channel device for guiding a heat carrier medium is formed in the mounting device in the seat region. A local channel system (heat pipe) that can be formed in the carrier element is embodied to assist heat transfer from the head region to the seat region, in combination with a phase change of the heat carrier medium introduced into this local channel system of the carrier element. For example, each of the mirror elements may form a mirror array.

The mirror arrangement described above can, for example, be used in an illumination system of a lithography apparatus for illuminating an object field provided with a reticle. This illumination system can be designed so that only two mirror arrangements with a plurality of micromirror elements are required. In this case, a first mirror arrangement in the beam path can be designed as a field-forming element in the form of a mirror reflector, and a second mirror arrangement in the beam path can be used to image the mirror reflector into the exit pupil of the illumination system, as described, for example, in patent document DE 10317667 A1. In particular, the first and second mirror arrangements can be designed as faceted mirrors.

Compared to illumination systems with at least three mirror arrangements, the illumination system described in DE 10317667 A1 offers the advantage of improved transmission and, therefore, higher productivity of lithography systems. In order to produce certain illumination settings, in particular in such illumination systems, if light reflected by the mirror elements in the first mirror arrangement reaches the object field of the illumination system, this has no effect on system performance.

In principle, a beam dump that provides unwanted radiation can be used to absorb light or radiation. For this purpose, patent document DE 10 2015 210 041 A1 proposes at least one thin-film arrangement using at least one reflective thin film. The thin-film arrangement is configured such that reflected light, directed toward the at least one beam dump, is incident on the thin-film arrangement at least intermittently during operation of the projection exposure apparatus and does not enter the light pipe used.

An object of the present invention is to provide a mirror arrangement that absorbs unwanted radiation and, in doing so, minimizes the impact on the optical properties of the mirror arrangement. Another object of the present invention is to provide a lithography system, in particular a lithography apparatus, having at least one such mirror arrangement. Subject of the Invention

According to a first aspect, the object is achieved by a mirror device of the aforementioned type, wherein, for absorbing incident radiation, at least one insertion opening does not accommodate a carrier element (and also does not accommodate a dummy carrier element), and/or wherein, for absorbing incident radiation, at least one of the insertion openings accommodates a dummy carrier element that does not carry a mirror element.

Therefore, the number of insertion openings in the mirror device according to the invention is greater than the number of carrier elements, to which mirror elements are attached, that are inserted into these insertion openings. At least one insertion opening that does not accommodate a carrier element can be used as a beam dump, and/or at least one dummy carrier element that does not carry a mirror element can be used as a beam dump. The dummy carrier element that does not carry a mirror element typically has a seat that is immersed in the insertion opening and is formed in the same or similar manner as the seat of the carrier element that carries the mirror element. In practice, the number of beam dumps, i.e., the number of insertion openings without carrier elements or the number of dummy carrier elements that do not carry mirror elements, can be specified as required within the production range of the mirror device, depending on the power consumption. In addition, since the carrier element is typically detachably connected to the mounting device, the number of beam dumps can be selectively changed after the mirror arrangement has been produced. Thus, individual carrier elements can be removed, or a carrier element carrying a mirror element can be replaced by a dummy carrier element that does not carry any mirror elements.

As mentioned above, a dedicated component in the form of a beam dump that is thermally decoupled from the mirror arrangement can, in principle, be used to absorb radiation. However, absorbing radiation using a separate component acting as a beam dump is not always possible, as the radiation to be absorbed needs to be directed to the beam dump. In the case where the mirror arrangement according to the invention is the second mirror arrangement of an illumination system, which is intended to absorb some of the radiation emitted by the first mirror arrangement of the illumination system so that it does not reach the reticle or the object field, a problem arises in that the mirror elements (typically in the form of micromirrors) in the first mirror arrangement can only be tilted by a relatively small angle when actuated. This often means that it is not possible to direct the unwanted radiation emitted by the first mirror arrangement to a separate beam dump that is thermally decoupled from the second mirror arrangement. Such a beam dump cannot be achieved because the switching range of the mirror element in the first mirror arrangement is limited. In order to direct the unwanted radiation to the beam dump, the switching range or angle over which the mirror element in the first mirror arrangement can be tilted must be increased; this is very problematic from a manufacturing perspective.

To absorb unwanted radiation, despite the limited switching range of the mirror elements in the first mirror arrangement, it is advantageous to place a beam dump on the mounting device of the second mirror arrangement, near the mirror elements in the second mirror arrangement. However, this arrangement heats up at the location of the beam dump and thus carries the risk of thermoelastic deformation. This reduces the positioning accuracy of the mirror elements in the second mirror arrangement, which are intended to reflect the incident radiation; as a result, the mirror elements no longer strike the intended position on the reticle or may drift thermally.

The reflector device according to the invention allows for the absorption of incident radiation without significantly affecting the optical properties of the reflector device in the process: the absorbed radiation can be effectively absorbed and dissipated at the insertion opening or at a dummy carrier element accommodated in the insertion opening, thereby preventing significant heating of the mounting device and thus thermal drift behavior of the reflector element.

To cool the insertion opening serving as a beam dump or the virtual carrier element serving as a beam dump, known concepts for cooling mirror elements can be used, such as described, for example, in the aforementioned patent document DE 10 2014 219 770 A1, the content of which is incorporated by reference in its entirety into the present invention. In the case of the aforementioned mirror arrangement, components already present in the mirror arrangement can be used to implement the beam dump. Consequently, there is no need to newly develop or manufacture a beam dump and the associated cooling concepts therefor. In particular, the same cooling arrangement or cooling system can be used to cool the mirror element serving as a beam dump and the insertion opening and/or the virtual carrier element serving as a beam dump. This allows the heat buildup of the mount in the area of the beam dump to be kept very low (on the same order of magnitude as the mirror element integrated there). Furthermore, an effective cooling system can be implemented, thereby minimizing thermal deformations of the mount and thus preventing thermal drift of the mirror element.

In one embodiment, the mirror arrangement includes at least one channel arrangement for guiding a coolant, which is formed in the region of at least one insertion opening in the mounting device that does not accommodate a carrier element, and/or in the region of the bottom of at least one dummy carrier element. The channel arrangement effectively dissipates heat from the insertion opening serving as a beam dump and/or the dummy carrier element. The temperature of the coolant guided through the channel arrangement can be adjusted so that it substantially corresponds to a target temperature of the mirror arrangement. For example, the channel arrangement can be implemented in the manner described in patent document DE 10 2014 219 770 A1 for cooling the corresponding mirror element. As described therein, the corresponding carrier element typically has a seat that is immersed in the insertion opening. However, in contrast to the carrier element described therein, no mirror element is attached to the head of the virtual carrier element acting as a beam dump; instead, the head acts as a beam dump for absorbing radiation.

In another embodiment, the inner wall of the at least one insertion opening is formed by a socket element embedded in the mounting device, preferably, the channel means for guiding the coolant is formed at least partially by a cutout extending in the outer region of the socket element.

As described in patent document DE 10 2014 219 770 A1, the channel means for guiding the coolant can be provided at least partially via a cutout extending in the outer region of the socket element, for example in the form of a hollow cone. Alternatively or additionally, a groove or channel structure can be formed that is configured to guide the coolant in the body forming the mounting device. The coolant can also be guided via a channel means formed directly in the mounting device or via a channel system connected to a channel means provided on part of the socket element. The channel means or channel system for guiding the coolant can also extend solely in the body of the mounting device, without requiring a socket element. For example, if the mounting device or its body is produced by additive manufacturing (e.g., using a 3D printing method), the socket element can be omitted. The channel system formed in the mounting device can be designed so that the surrounding areas of multiple insertion openings can be cooled in parallel. In particular, the channel system can be used to cool the surrounding areas of all insertion openings, that is, the insertion openings in which the mirror element is inserted and the insertion openings in which no carrier element is inserted or in which a dummy carrier element is accommodated.

In a further embodiment, at least one inner wall of the insertion opening, which does not accommodate a carrier element, has a radiation-absorbing coating and/or a radiation-absorbing surface structure. If no carrier element is accommodated in the insertion opening, the radiation which is not desired to be reflected by the reflector arrangement is essentially incident on the inner wall of the insertion opening, where it should be absorbed as effectively as possible. In principle, almost any material absorbs EUV radiation; that is, the absorbing coating or the absorbing surface structure on the inner side of the insertion opening does not necessarily need to be used for absorbing EUV radiation. However, the radiation incident on the reflector arrangement or the beam dump can also have a wavelength longer than the EUV wavelength range, for example, the wavelength radiation range is in the EUV, UV, VIS or IR wavelength range. Specifically, the wavelength of the radiation component generated by the EUV light source can be outside the EUV wavelength range and should not propagate within the lithography system.

Radiation in these wavelength ranges can be effectively absorbed, in particular, by providing a radiation-absorbing coating and/or a radiation-absorbing surface structure (e.g., in the form of appropriately formed microstructures). As mentioned above, the inner wall of the insertion opening can be formed by a socket element, the inner side of which is provided with an absorbing coating or an absorbing surface structure; however, this is not mandatory, i.e., the inner wall of the insertion opening can also be formed directly on the mounting device.

In another embodiment, at least one insertion opening that does not accommodate a carrier element is hermetically sealed, preferably at a distance from one end of the reflector element. As described in patent document DE 10 2014 219 770 A1, a corresponding carrier element is usually inserted into the socket element in a sealed (hermetically sealed) manner to hermetically seal the insertion opening. This allows a vacuum to be applied to the side of the reflector device on which the reflector element is located without causing gas to flow in from the rear area of the mounting device, wherein the vacuum is usually not applied via the connection area of the carrier element. If the insertion opening does not accommodate a carrier element, hermetically sealing the insertion opening is advantageous for the same reasons. This can be achieved, for example, by inserting a seal, for example in the form of a plug, into the aforementioned socket element, or by using a socket element with a can-shaped structure and a base that hermetically seals the insertion opening.

It is generally advantageous to hermetically seal the insert opening on the side remote from the reflector element, rather than on the side facing the reflector element, in order to maximize the utilization of the insert opening's inner wall area for beam dumping. Specifically, radiation components that initially strike the inner wall and are not absorbed but are also undesirably reflected can be reflected multiple times within the insert opening and strike the inner wall again, thereby completely absorbing them.

In another embodiment, at least one dummy carrier element has a head region that protrudes beyond the insertion opening. This head region preferably protrudes further beyond the insertion opening than the head region of the carrier element carrying the mirror element. Typically, the mirror element has a blocky or cuboid structure. In particular, if the mirror element is a MEMS mirror module (see below), its thickness is not negligible, as the control logic must also be incorporated into the mirror element in addition to the tiltable micromirrors. Therefore, for efficient radiation absorption by the dummy carrier element, it is advantageous if the head region of the dummy carrier element protrudes further beyond the insertion opening than in the case of the carrier elements carrying the mirror element. In particular, the head region or its end face can protrude beyond the insertion opening until the head region or its end face is approximately flush with the top end of the mirror element (in a non-tilted position).

In another embodiment, the dummy carrier element has an absorbing coating and/or an absorbing surface structure on a head region protruding beyond the insertion opening, in particular on the end faces of the head region. As mentioned above, this is particularly advantageous for absorbing incident radiation in a wavelength range longer than the EUV wavelength range. If the dummy carrier element is accommodated in the insertion opening, the dummy carrier element typically has a head region protruding beyond the insertion opening, and a majority of the radiation absorbed by the dummy carrier element is intended to be incident on this head region. The absorbing coating and/or the absorbing surface structure can be provided on the protruding head region, in particular on its end faces; however, this is not mandatory.

In another embodiment, at least one dummy carrier element has a solid structure at least in the head region, and in particular, throughout the entire head region. The solid structure of the dummy carrier element ensures effective heat dissipation. In contrast, the carrier element carrying the mirror element typically has through-channels for routing connection and control lines through the carrier element, thereby connecting the multiple actuators included in the mirror element to an electronic actuation system.

In one development, a closed channel system with an introduced coolant is formed in the virtual carrier element. The coolant preferably undergoes a phase change to transfer heat from the head region to the base of the virtual carrier element. The coolant in the closed channel system (perhaps in the form of water, for example) can absorb heat without changing its phase. The closed channel system with the introduced coolant, in this case in conjunction with the phase change, can transfer heat from the head region to the base of the virtual carrier element, for example, based on the principle of a heat pipe.

In an alternative development, the dummy carrier element has a channel system for guiding the coolant, comprising an inlet and an outlet for the coolant. In contrast to the embodiment described further above, the channel system is not closed in this case; in other words, the dummy carrier element is cooled directly. This minimizes or keeps the heat path from the heat source (the surface on which the radiation impinges) to the coolant as short as possible. Typically, the channel system of the dummy carrier element is designed to supply coolant to and remove coolant from the head region of the dummy carrier element.

In a development of this embodiment, the mirror device is designed to fluidically connect the inlet and outlet of the channel system to the channel device of the mounting device or to the channel device of a heat sink arranged adjacent to the mounting device.

In the first scenario described further above, the mounting device comprises a channel arrangement comprising a supply opening for supplying coolant to the inlet and a discharge opening for discharging the coolant from the outlet of the channel system of the virtual carrier element. For example, if the inlet and outlet of the channel system are formed at the bottom of the carrier element, the sealing between the virtual carrier element and the channel arrangement of the mounting device is achieved by radial seals; or, if the inlet and outlet are arranged in the head region of the carrier element and are laterally offset from the insertion opening, by means of axial seals.

In the second scenario described further above, the inlet and outlet are directly connected to the channel means of a heat sink arranged adjacent to the mounting device and are typically not fluid-tightly connected to the channel means of the mounting device. The fluid-tight connection of the inlet and outlet of the virtual carrier element to the channel means of the heat sink can be achieved with the aid of a sealing device. For example, the sealing device can be designed as an axial or radial seal.

In an alternative, the inlet and outlet of the dummy carrier element may be connected via lines (eg via pipes) to an external cooling device or an external cooling circuit to enable direct cooling.

As described in patent document DE 10 2014 219 770 A1, the (virtual) carrier element is preferably geometrically adapted to provide a cross-section that is sufficient for heat transfer and as large as possible, at least in the base of the immersion mount. Preferably, the carrier element is made of a material with good thermal conductivity and moderate, preferably as low a thermal expansion as possible. For example, copper, silicon, silicon carbide (SiC), molybdenum alloys, tungsten alloys, or stainless steel are problematic as materials. The base of the carrier element and the inner wall of the insertion opening are preferably conical or pyramidal in shape; however, this is not mandatory; for example, the base of the carrier element and the inner wall of the insertion opening can also be cylindrical.

For example, the coolant may be water, an aqueous mixture, glycol, a gas or gas mixture, or liquid CO ₂ , wherein a phase change from liquid to gas can be utilized in the gaseous state, such as described above in a heat pipe.

In another embodiment, the mirror element is in the form of a MEMS mirror module. A MEMS mirror module has a plurality of microelectromechanically actuatable mirrors, typically arranged in a grid (array). As described above, each mirror can be individually actuated and can typically be tilted about at least one axis, and typically about two axes. The number of mirrors in a MEMS mirror module can vary; for example, 24×24 or 25×25 mirrors can be arranged in a grid. The corresponding MEMS mirror module typically also includes logic elements and micromechanical structures in wafer form to control or actuate the mirrors.

In a further embodiment, the plurality of mirror elements is arranged in a grid, with at least one insertion opening for accommodating no carrier element and/or at least one insertion opening for accommodating a dummy carrier element being arranged at a side edge of the grid or between the mirror elements of the grid, in particular in the center of the grid. As already mentioned, it is advantageous if the insertion opening serving as a beam dump or the carrier element serving as a beam dump is arranged as close as possible to the mirror element in the mirror arrangement. This means that the switching range of the mirror elements of another mirror arrangement arranged upstream in the beam path does not need to be increased in order to direct the radiation reflected thereto to the corresponding beam dump of the mirror arrangement according to the invention. The beam dumps at the side edges of the grid are located at the outermost positions of the corresponding rows and/or columns of the grid. A beam dump at the edge of the grid is also understood to mean a beam dump that is placed next to a beam dump arranged at the outermost position. As an alternative or in addition to arranging the beam dump at the side edge of the grid, the beam dump can also be arranged distributed between the mirror elements of the grid, that is, not at the edge of the grid, but for example in the center or middle of the grid.

In the cooling concept described above, the corresponding carrier element carrying the mirror element or serving as a beam dump can be replaced without having to open or interrupt the cooling circuit in the process.

The fixing portion corresponding to the carrier element can be used to secure the (dummy) carrier element to the mounting device, and the retaining force that secures the carrier element in the mounting device is introduced into the carrier element via the fixing portion. For example, the fixing portion can be in the form of a threaded portion, on which a nut is mounted, which generates the retaining force when tightened. For example, the retaining force generated by the nut can be transmitted to the mounting device by including a spring. The pressing mechanism that presses the carrier element out of the mounting device from below can also be located in the area of the fixing portion.

Another aspect of the present invention relates to a lithography system, particularly a lithography apparatus, comprising at least one mirror arrangement as described above, wherein the mirror arrangement is preferably configured in an illumination system of the lithography apparatus. The lithography system may be a lithography apparatus for exposing wafers or some other optical device used in lithography, such as an inspection system, e.g., for inspecting lithography apparatus, wafers, etc. used in lithography. The lithography system may particularly be an EUV lithography system designed to utilize wavelength radiation within the EUV wavelength range, which is between 5 nm and 30 nm.

The illumination system can specifically have two mirror arrangements, wherein the first mirror arrangement in the beam path forms a mirror reflector, as described in the aforementioned patent document DE 10317667 A1, the content of which is incorporated herein by reference in its entirety. The illumination system can also have a different design and, for example, have three or more mirror arrangements. Specifically, the mirror arrangements can be in the form of faceted mirrors.

In one embodiment, a lithography system includes a further mirror arrangement having a plurality of further mirror elements, wherein the further mirror arrangement is arranged in the beam path upstream of the further mirror arrangement in the illumination system, and the plurality of further mirror elements are designed to radiate radiation to be absorbed at at least one insertion opening that does not accommodate a carrier element and/or at at least one insertion opening that accommodates a dummy carrier element. Furthermore, the further mirror arrangement is designed to radiate radiation to be reflected by the mirror elements of the mirror arrangement so as to radiate the radiation toward the object field or the reticle. For example, the further mirror elements of the further mirror arrangement may be MEMS mirror modules.

As already mentioned above, in this case, it is advantageous if the mirror element and the insertion opening serving as a beam dump or the virtual carrier element are arranged as close to one another as possible, so that the further mirror element in the further mirror arrangement does not need to be tilted too far in order to guide the radiation to be absorbed to the insertion opening serving as a beam dump or to the virtual carrier element of the mirror arrangement according to the invention.

Further features and advantages of the present invention will become apparent from the following description of working examples of the present invention, with reference to the accompanying drawings showing important details of the present invention, and the scope of the claims. In variations of the present invention, each feature can be implemented alone or in any combination in its own right.

The essential parts of an optical device for EUV lithography in the form of a projection exposure apparatus 1 (EUV lithography apparatus) are described below by way of example with reference to Figure 1. The description of the basic structure of the projection exposure apparatus 1 and its components should not be considered limiting.

An embodiment of an illumination system 2 of a projection exposure apparatus 1 comprises a light or radiation source 3 and an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

A reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle carrier 8. The reticle carrier 8 can be moved by a reticle displacement driver 9, in particular in the scanning direction.

For explanatory purposes, FIG1 depicts a Cartesian xyz coordinate system. The x-direction is perpendicular to the drawing plane. The y-direction extends horizontally, and the z-direction extends vertically. The scanning direction extends along the y-direction in FIG1 . The z-direction extends perpendicular to object plane 6 .

The projection exposure apparatus 1 comprises a projection system 10. The projection system 10 is used to image the object field 5 into an image field 11 in an imaging plane 12. The structures on the reticle 7 are imaged onto the photosensitive layer of a wafer 13 arranged in the region of the image field 11 in the imaging plane 12. The wafer 13 is held by a wafer carrier 14. The wafer carrier 14 can be moved, in particular in the y-direction, by a wafer displacement driver 15. On the one hand, the reticle 7 is moved by the reticle displacement driver 9, and on the other hand, the wafer 13 can be moved synchronously by the wafer displacement driver 15.

A radiation source 3 is an EUV radiation source. Specifically, the radiation source 3 emits EUV radiation 16, hereinafter also referred to as used radiation, illumination radiation, or illumination light. Specifically, the used radiation has a wavelength range of 5 nm to 30 nm. The radiation source 3 can be a plasma source, such as a laser-induced plasma (LPP) source or a gas discharge-induced plasma (GDPP) source. It can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

Illuminating radiation 16 emitted from radiation source 3 is focused by concentrator 17. Concentrator 17 can be a concentrator having one or more elliptical and/or hyperboloidal reflective surfaces. Illuminating radiation 16 can strike at least one reflective surface of concentrator 17 at grazing incidence (GI), that is, an angle of incidence greater than 45°, or at normal incidence (NI), that is, an angle of incidence less than 45°. Concentrator 17 can be structured and/or coated, primarily to optimize its reflectivity for the radiation being used and secondly to suppress extraneous light.

The illuminating radiation 16 propagates through an intermediate focus in an intermediate focus plane 18 downstream of the condenser lens 17. The intermediate focus plane 18 can constitute a separation between the radiation source module containing the radiation source 3 and the condenser lens 17 and the illumination optics unit 4.

The illumination optical unit 4 comprises a deflection mirror 19 and a first faceted mirror 20 arranged downstream thereof in the beam path. The deflection mirror 19 can be a plane deflection mirror or, alternatively, a mirror having a beam-influencing effect that goes beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be in the form of a spectral filter that separates the used light wavelength of the illumination radiation 16 from external light that deviates from this wavelength. The first faceted mirror 20 comprises a plurality of individual first facets 21, also referred to below as field facets. FIG1 illustrates only some of the facets 21 by way of example. A second faceted mirror 22 is arranged downstream of the first faceted mirror 20 in the beam path of the illumination optical unit 4. The second facet reflector 22 includes a plurality of second facets 23 .

The illumination optical unit 4 thus forms a double-faceted system. This basic principle is also known as a compound eye integrator. Each first facet 21 is imaged into the object field 5 by means of a second facet mirror 22. The second facet mirror 22 is the final beam shaper, or in fact the final mirror for the illuminating radiation 16 in the beam path upstream of the object field 5.

The projection system 10 includes a plurality of mirrors Mi, which are numbered consecutively according to their configuration in the beam path of the projection exposure apparatus 1.

In the example shown in FIG1 , projection system 10 includes six mirrors M1 to M6. Alternative examples with 4, 8, 10, 12, or any other number of mirrors M1 are also possible. The penultimate mirror M5 and the final mirror M6 each have a through-aperture for illuminating radiation 16. Projection system 10 is a double-shade optical unit. The image-side numerical aperture of projection optical unit 10 is greater than 0.4 or 0.5, and may also be greater than 0.6, for example, 0.7 or 0.75.

Like the reflector of the illumination optical unit 4 , the reflector Mi can have a highly reflective coating for the illumination radiation 16 .

FIG2 shows a partial cross-sectional view of a second faceted mirror arrangement 22 of the illumination system 2 of FIG1 . The mirror arrangement 22 comprises a plurality of mirror elements 23 arranged in close proximity, forming a concave surface, and aligned relative to the optical center. Each mirror element 23 is configured to reflect electromagnetic radiation, more precisely EUV radiation 16, which is reflected from a facet 21 of the first faceted mirror 20 in the illumination system 2 to the second faceted mirror arrangement 22. In the example shown, the mirror elements 23 are in the form of MEMS mirror modules. The corresponding MEMS mirror module has a plurality of micromirrors arranged in a grid (e.g., 25×25 micromirrors) and can be actuated on an individual basis for more precise tilting. To this end, the corresponding mirror element 23 in the form of a MEMS mirror module has logic components and micromechanical structures in the form of a chip.

The mirror device 22 shown in FIG2 also includes a plurality of carrier elements 24, each of which carries one of the mirror elements 23. The mirror device 22 also has a mounting device 25 comprising conical insertion openings 26 designed to receive corresponding ones of the conical carrier elements 24, each of which carries a corresponding mirror element 23. The mounting device 25 has a multi-part structure and comprises a plurality of frame shells assembled together in a layered manner. For details regarding the structure of the mirror device 22, how the carrier elements 24 are fastened to the mounting device 25, and the structure of the mounting device 25, please refer to patent document DE 10 2014 219 770 A1.

FIG3 shows a plan view of the mirror element 23 of the mirror arrangement 22 of FIG2 , more precisely its reflective surface or end face, which in the example shown has a square geometry. It will be appreciated that the mirror element 23 can also have a different geometry. As can also be seen from FIG3 , the mirror elements 23 are arranged in a grid 27 having a plurality of rows and columns. Each grid position, shown in dashed lines in FIG3 , also has an insertion opening 26 but is not provided with a mirror element 23, as can be seen at the side edges 27 a of the grid 27. The grid positions at the edges of the grid 27 shown in FIG3 serve as beam dumps for absorbing EUV radiation 16, which is reflected by the facets 21 in the first facet mirror 20 to the mirror arrangement in the form of the second facet mirror 22, but is not intended to reach the mask 7. In the case of certain lighting settings or operating states of the lighting system 2, radiation 16 reflected by certain facets 21 of the first facet reflector 20 at corresponding angular positions which are advantageously provided for this purpose is captured or absorbed.

Providing beam dumps at the side edges 27a of the grid 27 of the mirror element 23 is advantageous because the facets 21 in the first facet mirror 20 can be actuated (typically tilted), but the tilt angle that can be set during actuation is relatively small. Therefore, it is generally not possible to direct unwanted radiation 16 emanating from the facets 21 in the first facet mirror 20 to the beam dump arranged next to the second facet mirror 22. However, the switching range of the facets 21 in the first facet mirror 20 is sufficient to direct unwanted radiation to the left and right edges 27a, 27b of the grid 27 of the mirror element 23 in order to absorb radiation 16 incident thereon. Alternatively or additionally to the beam dumps being arranged at the side edges 27a, 27b of the grid 27, the beam dumps can also be placed in a distributed manner between the mirror elements 23 of the grid, for example in the center 27c of the grid 27, as shown in FIG.

In order to avoid a situation where the mounting device 25 is deformed during absorption of radiation 16 and the mirror element 23 no longer deflects the incident radiation 16 to the desired location on the reticle 7, it is necessary to effectively cool the mounting device 25 at the grid locations for absorbing radiation 16. Two options for effective cooling or heat dissipation are described below in conjunction with Figures 4a and 4b.

FIG4 a shows a beam dump in the form of an insertion opening 26 without a carrier element 24 and two adjacent insertion openings 26, each of which accommodates a carrier element 24 carrying a reflector element 23. As can be seen from FIG4 a, radiation 16 to be absorbed enters insertion opening 26 at the side of mounting device 25 facing reflector element 23 and is reflected multiple times at inner wall 26 a of insertion opening 26, where the majority of radiation 16 to be absorbed is absorbed. The geometry of inner wall 26 a of insertion opening 26 does not need to be conical as shown in FIG4 a; instead, it can be cylindrical or any other geometric shape.

In the example shown, the inner wall 26a of the insertion opening 26 has an absorbing coating 28 for absorbing incident radiation 16. Alternatively or additionally, the inner wall 26a of the insertion opening 26 can have an absorbing surface structure. In the example shown, the absorbing coating 28 is designed to absorb radiation generated by the light source 3 with a wavelength longer than 30 nm, such as radiation in the VUV, UV, VIS, or IR wavelength ranges. Even without the absorbing coating 28 or surface structure, the material of the inner wall 26a of the insertion opening 26 would absorb a significant portion of the incident radiation 16 in the EUV wavelength range.

Based on Kirchhoff's law for thermal radiation, the following formulas apply to emissivity ε (in this case, the absorption of incident radiation by the beam dump), reflection δ, and transmission τ (in each case expressed in %): ε + δ + τ = 1. All three parameters depend on the wavelength and angle of incidence of the incident radiation 16; these dependencies are ignored in the following considerations to simplify the situation. The effective emissivity εeff of the beam dump for incident radiation 16 (corresponding to the effective absorption by the beam dump) depends not only on the emissivity ε of the beam dump for the corresponding reflection at inner wall 26a, but also on the number n of reflections at inner wall 26a. In this case, the effective emissivity εeff of the beam dump should be as close to 1 as possible so that the radiation 16 falling on the beam dump is converted as completely as possible into heat, which can be removed by a cooling device.

The effective emissivity εeff of the beam dump can be estimated using the following formula: εeff = 1 – (1 -ε)n. In this formula, the effects of the angle of incidence are neglected, and the transmittance τ = 0 is assumed. For example, if the emissivity ε of the beam dump for the entire incident radiation 16 (averaged over radiation in the EUV wavelength range and other wavelength ranges) is assumed to be approximately 35% in the case of reflection at the inner wall 26a, and if n = 3 reflections is assumed, then the effective emissivity is as follows: εeff = 72.5%. As described above, in this case, the emissivity ε is averaged over all wavelengths of the incident radiation 16. The emissivity ε of the incident radiation 16 in the EUV wavelength range, and therefore the effective emissivity εeff of the beam dump, is significantly higher than the values calculated here.

To effectively dissipate the absorbed radiation 16, the mounting device 25 has a channel arrangement 29 in the form of a channel system for guiding a coolant 30, which in this case is water. Alternatively, other coolants can be used, such as aqueous mixtures, glycol, gases or gas mixtures, or (liquid) _CO₂ . In the example shown in FIG4a , the inner wall 26a of the insertion opening 26 is formed by a socket element 31 embedded in the mounting device 25. In the example shown, the channel arrangement 29 for guiding the coolant 30 is formed at least partially by cutouts 29a extending in the outer region of the socket element 31. For details on the design of the channel arrangement 29 and its interaction with the socket element 31, reference is made to patent document DE 10 2014 219 770 A1.

At the end of the conical socket element 31 remote from the reflector element 23, a seat 31 a hermetically seals the insertion opening 26. This allows a vacuum to be applied to the side of the reflector device 22 on which the reflector element 23 is located, without the air flow from the rear region of the mounting device 25 being able to reach the front side of the reflector device 22 through the insertion opening 26. As an alternative to the solution shown in FIG4 a, a seal in the form of a plug or the like can be used to hermetically seal the insertion opening 26. The carrier element 24 is also inserted into the corresponding socket element 31 in order to seal the socket element 31. An O-ring 32 is inserted into a corresponding annular groove in the carrier element 24 to achieve a seal via the seal in the form of the O-ring 32.

FIG4 b shows a diagram similar to FIG4 a , in which the beam dump is implemented by a virtual carrier element 24 ′ which, in contrast to the two other carrier elements 24 shown in FIG4 b , does not carry a mirror element 23. The virtual carrier element 24 ′ serving as a beam dump has a base 33 that projects into the insertion opening 26 and a head region 34 ′ that projects beyond the insertion opening 26 in the direction of the mirror element 23. The head region 34 ′ projects further beyond the insertion opening 26 than the head regions 34 of adjacent carrier elements 24, each of which carries a mirror element 23. The further projecting head region 34 ′ has an end face 35 that terminates flush with the end face or reflective surface of the adjacent mirror element 23. This and the provision of an absorbing surface structure 36 on the end face 35 of the head region 34' allow radiation 16 incident on the head region 34' of the dummy carrier element 24' to be effectively absorbed. The absorption of incident radiation 16 at the end face 35 of the head region 34' should be greater than 70%.

To effectively dissipate the heat absorbed from the head region 34' of the virtual carrier element 24', a closed channel system 37 is formed in the virtual carrier element 24', more precisely in the seat 33, with an introduced coolant 38. This coolant cooperates with the phase change to transfer heat from the head region 34' to the bottom 33 of the virtual carrier element 24' (a so-called heat pipe). For example, the coolant 38 can be _CO2 . Alternatively, the coolant 38 in the closed channel system 37 may not change its phase. As can be seen from FIG4b , the closed channel system 37 is confined to the bottom 33 of the virtual carrier element 24′; that is, the head region 34′ of the virtual carrier element 24′ has a solid structure, but this is not mandatory. In contrast, the carrier element 24 carrying the mirror element 23 has a through-channel 39 for routing connection and control lines through the carrier element 24, thereby connecting the actuator included in the mirror element to the electronic actuation system.

Unlike FIG4 b , the virtual carrier element 24 ′ can also have a completely solid structure, that is, without a cavity. In both cases, the virtual carrier element 24 ′ can be cooled in the manner described in the entire text of FIG4 a , that is, by means of a channel arrangement 29 designed to guide the coolant 30 and formed in part by cutouts 29 a extending in the outer region of the socket element 31. However, the use of a socket element 31 is not mandatory.

FIG4c shows a diagram similar to FIG4a , in which the beam dump is formed by an insertion opening 26 that does not accommodate the carrier element 24, which in the example shown is cylindrical. In the mirror arrangement 22 shown in FIG4c , the mounting device 25 is produced by layer-by-layer manufacturing using a 3-D printing method. During the production of the mounting device 25, the channel arrangement 29 for guiding the coolant 30 is already introduced in the form of a cavity into the material of the mounting device 25 or its body. The provision of the socket element 31 or the cutout 29a can be omitted in the mirror arrangement 22 shown in FIG4c . It should be understood that the virtual carrier element 24′ described in FIG4b can also be used as a beam dump in the case of the mirror arrangement 22 shown in FIG4c .

In an alternative to the exemplary embodiment depicted in FIG4 b , the channel system 37 ′ of the dummy carrier element 24 ′ may not be closed, but may instead have an inlet 40 for the coolant 38 and an outlet 41 for the coolant 38, as shown in FIG5 a and b , which each illustrate a detail of the mirror device 22. In the example shown in FIG5 a and b , the channel system 37 ′ of the dummy carrier element 24 ′ is not fluidically connected to the channel device 29 of the mounting device 25 via the inlet 40 and the outlet 41.

In the example shown in FIG5 a , coolant 38 is supplied to an inlet 40 formed on a fixing portion 42 of the virtual carrier element 24′, which protrudes beyond the insertion opening 26, is discharged from an external cooling device via a supply line (not shown here), and is discharged from an outlet 41 via a discharge line (not shown here) and transported to an external cooling device. Outlet 41 is also formed on a fixing portion 42 of the virtual carrier element 24′, which protrudes beyond the insertion opening 26.

In the example shown in FIG5b , a heat sink 43 having a channel system 29 similar in form to the channel system 29 of the mounting device 25 is arranged adjacent to the mounting device 25. The channel system is designed to supply coolant 38 to the inlet 40 of the dummy carrier element 24′ and to discharge the coolant from the outlet 41 of the dummy carrier element 24′. By directing the coolant 38 through the additional heat sink 43, thermal deformation of the mounting device 25 can be reduced. In the case shown in FIG5b , it may be advantageous or necessary to seal the inlet 40 and outlet 41 with seals (not shown here). Radial and/or axial sealing concepts may be used for this purpose. With appropriate design of corresponding seals, for example in the form of suitable adapters or the like, the dummy carrier element 24′ can optionally be replaced without interrupting the flow of coolant 38 for this purpose. Specifically, when the dummy carrier element 24′ is secured in the mounting device 25, a fluid-tight connection can be established between the inlet 40 and the outlet 41 and the channel device 29 of the heat sink 43.

Unlike shown in Figures 5a and 5b, the inlet 40 and outlet 41 of the channel system 37' of the virtual carrier element 24' can also be fluidically connected to the channel means 29 of the mounting device 25. In this case, the inlet 40 and outlet 41 are not attached to the fixing portion 42 of the virtual carrier element 24', but are, for example, located on the side of the bottom 33 of the virtual carrier element 24', opposite the inner side 26a of the insertion opening 26. In this case, the socket element 31 shown in Figure 4b can be omitted. In this case, the supply opening of the channel means 29 of the mounting device 25 opens into the annular space formed between the virtual carrier element 24' and the inner side 26a of the insertion opening 26. In this case, the channel means 29 of the mounting means 25 also has a discharge opening for the coolant 38, which opens into the (further) annular space into which the outlet 41 of the virtual carrier element 24' opens. The annular space can be sealed by means of a radial seal, for example in the form of an O-ring or the like.

Alternatively, the inlet 40 and outlet 41 of the channel system 37' of the virtual carrier element 24' can also be formed in the head region 34' of the virtual carrier element 24', specifically, on the side of the head region 34' facing the mounting device 25, laterally offset from the insertion opening 26. In this case, the supply opening and discharge opening of the channel system 29 of the mounting device 25 open into corresponding gaps, into which the inlet 40 and outlet 41 of the channel system 37' of the virtual carrier element 24' respectively open. In this case, each gap can be sealed from the surrounding environment by an axial sealing device.

1: Lithography system 2: Illumination system 3: Radiation source 4: Illumination optical unit 5: Object field 6: Object plane 7: Reticle 8: Reticle carrier 9: Reticle shift actuator 10: Projection system 11: Image field 12: Image plane 13: Wafer 14: Wafer carrier 15: Wafer shift actuator 16: Radiation 17: Condenser lens 18: Intermediate focal plane 19: Polarizer 20: First facet mirror 21: First facet 22: Mirror assembly 23: Mirror element 24: Carrier element 24': Dummy carrier element 25: Mounting device 26: Insertion opening 26a: Inner wall 27: Grid 27a: Side edge 27b: Side edge 27c: Center 28: Absorbent coating 29: Channel arrangement 29a: Cutout 30: Coolant 31: Socket element 31a: Base 32: O-ring 33: Seat 34: Head area 34': Head area 35: End face 36: Absorbent surface structure 37: Channel system 37': Channel system 38: Coolant 39: Through channel 40: Inlet 41: Outlet 42: Mounting section 43: Heat sink M1: Reflector M2: Reflector M3: Reflector M4: Reflector M5: Reflector M6: Reflector

Exemplary embodiments are illustrated in schematic diagrams and explained in the following embodiments; Figure 1 shows a schematic longitudinal cross-section of a projection exposure apparatus for EUV projection lithography, the apparatus having an illumination system with two faceted mirrors; Figure 2 shows a perspective view of a mirror arrangement in the form of a second faceted mirror of the illumination system of Figure 1; Figure 3 shows a schematic plan view of the mirror elements of the faceted mirror of Figure 2, the mirror elements of the faceted mirror being arranged in a grid, wherein a plurality of beam dumps for absorbing radiation are arranged at the side edges and in the center of the grid; Figure 4a shows a schematic diagram of the mirror arrangement of Figure 3, having a beam dump in the form of an insertion opening without a carrier element; Figure 4b shows a schematic cross-sectional view of the mirror arrangement of Figure 3 , including a beam dump in the form of a virtual carrier element without a mirror element. Figure 4c shows a schematic cross-sectional view similar to Figure 4a , including a mounting device produced by 3D printing. Figures 5a and 5b show schematic views of a virtual carrier element into which a channel system having an inlet and an outlet for a coolant is introduced. In the following descriptions of the figures, identical reference numerals are used for components that are identical or have identical functions.

16: Radiation 23: Reflector element 24: Carrier element 24': Dummy carrier element 26: Insertion opening 26a: Inner wall 28: Absorbent coating 29a: Cutout 30: Coolant 31: Socket element 31a: Base 32: O-ring 33: Seat 34: Head area 34': Head area 35: End face 36: Absorbent surface structure 37: Channel system 38: Coolant 39: Through channel

Claims (15)

A mirror device for a lithography system comprises: a plurality of mirror elements for reflecting radiation; a plurality of carrier elements, each of which carries one of the mirror elements; a mounting device having a plurality of insertion openings for receiving a corresponding one of the carrier elements, each of which carries one of the mirror elements, and the carrier elements are received in the insertion openings of the mounting device; wherein, to absorb the radiation, at least one of the insertion openings does not receive the carrier element; and/or to absorb the radiation, at least one of the insertion openings receives a dummy carrier element, the dummy carrier element not carrying the mirror element. The reflector device as described in claim 1 further includes a channel device for guiding a coolant, and the channel device is formed in the area of at least one of the insertion openings of the mounting device that does not accommodate the carrier element and/or the seat of at least one of the virtual carrier elements. A reflector device as described in claim 1 or 2, wherein an inner wall of at least one of the insertion openings is formed by a socket element embedded in the mounting device, and the channel device for guiding the coolant is preferably formed at least partially by an incision extending in the outer area of the socket element. The reflector device as described in claim 1, wherein the inner wall of at least one of the insertion openings that does not accommodate the carrier element has a radiation absorbing coating and/or a radiation absorbing surface structure. A reflector device as described in claim 1, wherein at least one of the insertion openings that does not accommodate the carrier element is hermetically sealed and is hermetically sealed at an end away from the reflector element. A reflector device as described in claim 1, wherein at least one of the dummy carrier elements has a head area protruding beyond the insertion opening in the direction of the reflector element, and the head area protrudes further beyond the insertion opening than the head area of the carrier element supporting the reflector element. The reflector device of claim 1, wherein the dummy carrier element has an absorbing coating and/or an absorbing surface structure on the head region protruding beyond the insertion opening. A reflector device as described in claim 6 or 7, wherein at least one of the dummy carrier elements has a solid structure at least in the head area. A reflector device as described in claim 6 or 7, wherein a closed channel system is formed in the dummy carrier element and a coolant is injected, the coolant cooperating with the phase change to transfer heat from the head area to the seat of the carrier element. The mirror device of claim 1, wherein the dummy carrier element has a channel system for guiding the coolant, the channel system including an inlet and an outlet for the coolant. A reflector device as described in claim 10, which is designed to connect the inlet and the outlet of the channel system fluid-tightly to the channel device of the mounting device, or fluid-tightly connect to a channel device of a heat sink adjacent to the mounting device. A mirror device as described in claim 1, wherein the mirror element is in the form of a MEMS mirror module. A reflector device as described in claim 1, wherein the multiple reflector elements are arranged into a grid, wherein at least one insertion opening that does not accommodate the carrier element and/or at least one insertion opening that accommodates the dummy carrier element is arranged at a side edge of the grid or between the reflector elements (23) of the grid. A lithography system comprises: at least one reflector device as described in any of the preceding claims, wherein the at least one reflector device (22) is arranged in an illumination system (2) for illuminating a mask (7). The lithography system of claim 14 further comprises another mirror arrangement having a plurality of additional mirror elements, wherein the another mirror arrangement is arranged in the illumination system in the beam path upstream of the mirror arrangement, and the plurality of additional mirror elements are designed to emit radiation that is absorbed at at least one insertion opening that does not accommodate a carrier element and/or at at least one insertion opening that accommodates a dummy carrier element.